1. Field of the Invention
The present invention relates to a method of testing a secondary battery, particularly a secondary battery such as a lead storage battery or a nickel cadmium battery cell.
2. Description of the Related Art
Equipment, such as communications equipment, which is required to operate during a power outage, is provided with an UPS (uninterruptible power supply). As a result, the operation of the equipment is ensured even in the event of a power failure.
The UPS uses a lead storage battery or a nickel cadmium battery cell as a secondary battery. The lead storage battery has superior economy and energy efficiency when it is charged and discharged, and it is also easy to handle. Because of these advantages, it is widely used. Particularly, the lead storage battery is used in an UFS having large capacity. On the other hand, the nickel cadmium battery cell has long life and superior overcharge and overdischarge characteristics. Further, it is easy to maintain such a battery cell. For these reasons, it is widely used in compact equipment.
Particularly in the case of business equipment, it is commonly practiced to periodically replace the battery with a new one so as to ensure predetermined electrical capacity, because the secondary battery has an indefinite life span.
The electrical capacity of a plurality of lead storage batteries attached to the UPS is tested by discharging the batteries in parallel and by measuring resultant discharge characteristics. Unless predetermined electrical capacity is obtained, the batteries will be replaced with new ones. This test is intended to ensure continuous use of the batteries by checking them in a Predetermined manrer. Because the lead storage battery has unstable characteristics, due to the fact that it utilizes a chemical reaction, it is difficult to continuously assure the initial performance of the battery.
The battery test is carried out in the following manner:
Specifically, one of the plurality of lead storage batteries connected in parallel to a load is discharged, and that battery is then recharged. The discharging of each of the batteries is started at a slightly different time, and the thus discharged batteries are respectively recharged. The electrical capacity of the battery is checked by means of the discharge characteristics of each battery obtained as a result of the test. More specifically, as shown in FIGS. 1a-1c, given that a lead storage battery X and a lead storage battery Y are connected together, the lead storage battery X is discharged between a point in time "a" and a point in time "b". Then, the charging of the lead storage battery X is started from the point in time "b" and is completed at a point in time "d". On the other hand, the discharging of the lead storage battery Y is started at the point in time "b" and is finished at the point in time "c". The recharging of the lead storage battery Y is then started at the point in time "c" and is finished at a point in time "e".
The periodic replacement of the secondary battery may result in the waste of a usable battery and the unnecessary replacement of the battery. Therefore, it is desired that the battery judged as still being usable by a predetermined test continue to be used.
According to the above described conventional method, a lead storage battery is charged after having been discharged. However, in this method, the discharging of another battery is started before the charging of the current lead storage battery has been fully completed. As can be seen from total electrical capacity shown in FIG. 1c, the electrical capacity of the lead storage battery continues to drop over a long period of time, which makes it difficult to ensure predetermined electrical capacity.
In the case of a battery using a nickel electrode such as a nickel cadmium battery cell or a nickel hydrogen battery cell, a so-called memory effect, which produces a two-stage discharge curve, occurs when the battery is rapidly discharged after having been repetitively charged and discharged by only small amounts. If the above described lead storage battery testing method is applied to a battery such as a nickel cadmium battery using a nickel electrode, predetermined electrical capacity of the battery might not be obtained as a result of the memory effect.